Disable dashboard email deliveries

We have to doble check all emails deliveries from the dashboard.

Using a setting to skip all dashboard email deliveries for now.

Note that a rake task to activated the `Setting["dashboard.emails"]` will need to be addded when we want to activate deliveries of these emails.

db/dev_seeds/settings.rb

@@ -82,4 +82,6 @@ section "Creating Settings" do
   Setting.create(key: "proposals.poll_link", value: nil)
   Setting.create(key: "proposals.email_short_title", value: nil)
   Setting.create(key: "proposals.email_description", value: nil)
+
+  Setting.create(key: "dashboard.emails", value: nil)
 end